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In anticipation of the Blu-ray release of Ender’s Game, Home Theater Forum was invited to a press event at Digital Domain’s Los Angeles facility. The event covered the motion capture effects that were used to create the convincing zero gravity environments and combat seen in the movie. We were shown a series of presentations in an upstairs conference room, going over designs, previsualizations, on-set footage and completed visual effects. There were some fascinating areas that wound up in the discussion, including an analysis of the physics of the Battle Room environment and the difficulties in simulating a zero-gravity situation while in the Earth’s gravitation. Following the upstairs discussion, the group proceeded downstairs to a motion capture volume space, where we were given the opportunity to try shooting a rough mo-cap scene with the computers showing the animated version of our work on a big screen nearby. We were also given the chance to harness into a floating rig, which is the way the actors were suspended to simulate weightlessness. Some of us were better than others at the gymnastics. (Sadly, I was not one of the better performers here…)
The event began upstairs with production designer Ben Procter discussing the early design phase of the production of Ender’s Game. Procter showed us a 45 second previsualization teaser that was prepared around June 2011, showing a rough pass at young combatants suiting up and jumping out into the zero gravity Battle Room. This teaser was intended to whet the appetites of distributors and funders and get the movie about 40 million dollars of pre-sales, which would in turn fund the production. The teaser was successful, both in raising the funds and in giving Procter, director Gavin Hood, and the rest of the team a chance to start working out the designs that would wind up in the finished film. Procter discussed the issues with translating the Orson Scott Card novel into a feature film. Limiting our discussion to the spherical Battle Room itself, Procter described the decision to make the Room a transparent environment for the movie, which is a change from the book, where the room is opaque. The design of the dome evolved so that the solid discs at either end of the dome were reconceived to be mesh structures, again allowing viewers to see through them.
Procter showed multiple passes at shots with and without CGI – illustrating that the environment of the space station was accomplished via a combination of practical set pieces and CGI extensions. In the case of the Battle Room, nearly everything was CGI, but the actors were given limited set pieces they could touch, including some star-shaped objects on which they could land or bounce. A small portion of a window was also included for one shot where an actor needed to touch it. The rest of the actual set for the actors was a complete greenscreen environment, with the actors suspended in harnesses – sometimes in coordinated groups.
Visual effects supervisor Matt Butler than continued the discussion, providing more footage, including storyboards and further previsualization – this time of the Salamander Battle. Butler is the one who raised the issue that motion capture is not completely helpful when it comes to simulating zero gravity situations. This is due to the fact that the performer is still in a full gravity environment, so even if you suspend them in a rig, their hair will hang down and their body’s natural tendency will be to fall at any point that isn’t held up by the rig. This is why you see the actors’ arms and legs hanging down in these situations at any point that they relax. As a result, roughly 95 percent of the Battle Room shots seen in the finished film are CGI. Butler showed us a “how-to” movie that demonstrated how they would use the mo-cap footage for reference but would replace everything but the actors’ faces.
Butler described three signals of the problem people have with simulated zero gravity shots. The first has to do with the motion of centric mass. The idea is that due to gravity, if you throw an object, the center of the object will lower on an arc toward the ground as gravity pulls it down. In zero gravity, the object would just keep going straight, since there is no force to pull it downward. For this reason, some CGI was applied to modify the movements of the actors to keep them afloat and not show them being pulled to the floor. The second signal has to do with the pendulum effect, where a swinging object will swing back and forth while being pulled downward until settling at its lowest point – this is what you see with arms and legs hanging down, hair hanging down, etc. So the effects team uses CGI to replace the lower swinging elements with others that stay aloft. Finally, there is a concept of how gravity affects a person’s center of mass as they move in space. If a person is spinning, for example, their pick point will be at their center – which will look markedly different in zero gravity. If a person were doing that on Earth, they would be essentially held and supported by the center of their body, as they are quite literally grounded. This also applies if the person is suspended in the air – since they are still being pulled toward the ground by their own weight and mass. In a zero gravity environment, that spin would look completely different, since there would be nothing to pull them in any particular direction.
Around this time, director Gavin Hood arrived into the discussion and brought our group down to what was once the stage floor of the facility. (In years past, this complex has been the home of multiple television series and movies, including one I worked nearly ten years ago, E-Ring. These days, the facility is operated by Digital Domain, which really doesn’t do any filming here. I was told the actual shooting was all done in Louisiana, where Digital Domain has a large facility.) For what appears to be preparation and research purposes, Digital Domain maintains what is called a motion capture “volume” in the middle of the stage area. For those who are unfamiliar with the terminology, a “volume” is a large cube structure, with a large number of cameras rigged to the various horizontal and vertical pipes. Actors are outfitted with special form-fitting suits that allow the multiple cameras to essentially pick up the outline and pattern of their movement. Actors’ faces are decorated with black dots at key muscle points around the mouth, eyes, and other facial areas. An additional camera is then mounted to the actor’s head, getting a full face shot and capturing how the actors’ muscles move. When combined, the cameras collect a wide net of movement and performance data that are fed into the effects team’s computers and then applied to whatever CGI characters and creatures are intended.
As you can see from this photo, our event, the group was presented with a stunt actor wearing a black mo-cap suit, a small table set piece and a handheld digital camera with an onboard monitor that played back the team’s depiction of a virtual fantasy environment. A large TV screen was set up nearby so that the waiting journalists could see in real time what each prospective cameraman was accomplishing. Gavin Hood then directed each of us to do an approaching shot toward the stuntman and the table with a specific move that would end with the fantasy character turning his head to his right toward the camera lens. Footage was recorded of me performing this shot, but at this time I am unable to translate it to the appropriate codec for uploading here. If I can get past the snafus, I’ll post it for you. In the meantime, I hope that the above photograph will help give you the flavor.
Following the camera exercise, the journalists were encouraged to try our luck at the rig you see above. Initially, stunt player Moises Arias demonstrated how actors and stuntmen can simulate zero gravity moves by flipping themselves around while being suspended a few feet off the deck. If you really think about it, the actual physics are pretty simple here. You put on a harness, the harness gets attached the above rig, and then two strong stuntmen at the other end of the floor pull on two ropes that hoist you off the deck. At this point, you’re suspended in midair, whereupon you have the ability to spin yourself around and potentially flip yourself forwards or backwards. As I said, some of us were better at this than others. I can’t claim to be one of them – although I did fulfill a promise to the other journalists to say something memorable while trying to flip over. (I believe it was something along the lines of “the things I do for this site…”) For the record, if you’re ever in the position of simulating weightlessness while being hoisted aloft in this kind of harness, if you’d like to flip all the way over, you want to try to throw your arms forward and kick yourself in the back of the head. Let me know how it works out – it didn’t play out that well for me. On the other hand, since I’m currently unable to upload the file, this may spare you my indignation.
Looking at the event in total, this was a fascinating demonstration of motion capture technology and the philosophy behind it – particularly as applies to the simulation of weightlessness within our Earthbound plain. On behalf of Home Theater Forum, I thank Lionsgate, Gavin Hood and our hosts for inviting us to the event. Enders’ Game was released on Blu-ray and DVD on February 11th.
